The present invention relates generally to plasma cutting systems and, more particularly, to a controller for use with such systems.
Plasma cutting is a process in which an electric arc is used for cutting a workpiece. Plasma cutters typically include a power source, an air supply, and a torch. The torch, or plasma torch, is used to create and maintain the plasma arc that performs the cutting. A plasma cutting power source receives an input voltage from a transmission power receptacle or generator and provides output power to a pair of output terminals, one of which is connected to an electrode and the other of which is connected to the workpiece. An air supply is used with most plasma cutters to carry and propel the arc to the workpiece and help cool the torch.
There are multiple ways of initiating this cutting process, for example contact starting or high frequency or high voltage starting. Generally, in contact start plasma cutters, a movable or fixed electrode or consumable serves as a cathode and a fixed or movable nozzle or tip serves as an anode. In some units, the air supply is used to force a separation of the electrode and tip to create an initial or pilot arc. In others, mechanical or electromechanical means serve to separate the contacts and generate the pilot arc. In either case, once the pilot arc is established, air is forced past the pilot arc whereby it is heated and ionized to form a plasma jet that is forced out of the torch through the opening in the nozzle. The air aids in extending the arc to the workpiece forming a cutting arc and initiating the cutting process.
Both the pilot arc and the cutting arc are electrically supported by the electrode of the plasma torch. Due to the considerable heat and power concentration associated with the plasma cutting arc, the electrode commonly includes an insert supported in a body of the electrode. This insert, as compared to the body of the electrode, is generally formed of a material that is more impervious to wear associated with supporting the arc. The material of the insert is generally hafnium or zirconium based and can support repeated pilot and cutting arc generation and support. Although the insert is better equipped to support the plasma arc than the body of the electrode, it is still susceptible to wear.
During a cutting process, the cutting arc swirls about an end of the insert. The end of the insert liquefies due to the current and temperature associated with supporting the arc. After completion of a cutting process, the arc collapses and the movable contacts of the plasma torch must return to an idle position in preparation of a subsequent arc demand. To achieve the idle position, the movable contacts must come into contact or engage one another. Moving the contacts of the plasma torch from a separated or operating position to a contacting idle position results in an impact between the parts as they engage one another. This impact dislodges a portion of the liquefied material of the insert and expedites wear of the insert.
Additionally, during operation of the plasma torch, gas passes through the torch. A portion of this gas is converted to plasma to effectuate the plasma cutting process and another portion of the gas can be used to shield the plasma cutting process from surrounding conditions and to cool the components of the plasma torch. Upon completion of a cutting process, when the cutting arc collapses, the flow of gas through the plasma torch is also disrupted. The disruption of the gas flow through the plasma torch creates a pressure differential within the torch. This pressure differential within the torch also detrimentally affects retention of the liquefied portion of the insert. That is, the relatively sudden pressure change effectively sucks or blows a portion of the liquefied material from the insert. The sudden pressure change and the mechanical movement of the components of the plasma torch, individually and in combination, shorten the life cycle of the insert by removing that portion of the insert liquefied during a cutting process. Such operation increases consumable component consumption resulting in increased cost and decreased operational efficiency.
It would, therefore, be desirable to design a plasma cutting system that controls the plasma torch to allow solidification of the portion of the electrode insert liquefied during a plasma cutting operation.